Amazon advertising comes with its own language – TACoS, ROAS, CTR. But if there’s one metric sellers obsess over the most, it’s ACOS. And for good reason. Advertising Cost of Sales (ACOS) tells you, in a single percentage, how much you’re spending on ads to generate sales. Get it under control, and ads become a profitable growth channel. Ignore it, and you risk sinking margin into clicks that never pay back.
This guide breaks down exactly what ACOS is, how to calculate it, what “good” looks like, and strategies to bring it down without throttling growth.
What is ACOS?
ACOS stands for Advertising Cost of Sales. It measures the efficiency of your ad spend on Amazon. The formula is straightforward:
ACOS = (Ad Spend ÷ Ad Revenue) x 100
For example, if you spend £200 on ads and generate £1,000 in sales from those ads, your ACOS is 20%. That means you spent 20p for every £1 of revenue.
A lower ACOS generally means your ads are more efficient, but the “right” number depends heavily on your goals.
What Does a Good ACOS Look Like?
Here’s the nuance: there isn’t a universal “good” ACOS. It depends on factors like:
- Margins: If your product margin is 30%, you can sustain a higher ACOS than if your margin is only 10%.
- Business goals: Are you optimising for profit, or are you willing to break even to drive sales velocity and organic ranking?
- Product lifecycle: Launch campaigns often tolerate higher ACOS to gain reviews and traction. Mature products usually aim for lower ACOS to maximise profit.
As a general rule of thumb, many sellers target an ACOS that sits below their profit margin. If your margin is 25%, keeping ACOS under 25% ensures you’re not losing money. But in practice, the “sweet spot” varies.
The Difference Between ACOS and TACoS
While ACOS focuses purely on ad-attributed sales, TACoS (Total Advertising Cost of Sales) includes both ad-driven and organic sales. Why does this matter? Because effective advertising should lift your organic ranking over time. If ACOS looks high but TACoS is falling, you may still be moving in the right direction.
Tracking both gives a fuller picture. ACOS shows short-term efficiency. TACoS reveals long-term impact.
How to Calculate Your Break-Even ACOS
Before you can decide whether your ACOS is healthy, you need to know your break-even point. The formula is:
Break-Even ACOS = Profit Margin (%)
So if your margin is 30%, your break-even ACOS is 30%. Anything below that is technically profitable. Anything above means you’re spending more on ads than you’re making back in profit.
Knowing this number grounds your strategy. It stops you from chasing an arbitrary “low ACOS” and helps you decide whether a campaign is sustainable.
Common Reasons for High ACOS
If your ACOS feels too high, the cause usually falls into one of these buckets:
- Broad targeting: Keywords are too general, attracting irrelevant clicks.
- Weak listing: Even with good traffic, poor images or copy lead to low conversions.
- Too many non-converting terms: Campaigns haven’t been refined with negatives.
- Overbidding: Competing aggressively on expensive keywords without enough return.
- No segmentation: Multiple products crammed into one campaign muddy the data.
The good news: every one of these issues can be fixed.
Strategies to Reduce ACOS
- Tighten Keyword Targeting: Shift budget to high-performing exact match terms. Use auto campaigns for discovery but move winners into manual campaigns.
- Add Negative Keywords: Eliminate irrelevant search terms that drive clicks without conversions.
- Improve Listing Quality: Ads can only convert if your listing does the heavy lifting. Invest in strong main images, clear titles, persuasive bullets, and reviews.
- Adjust Bids Strategically: Don’t blindly cut bids across the board. Lower bids on underperformers, but increase where conversion data proves profitability.
- Use Placement Adjustments: Increase bids for “Top of Search” if those placements convert better, while reducing bids elsewhere.
- Balance Funnel Spend: Don’t sink all your budget into broad awareness ads if profitability is the immediate goal. Lean more into Sponsored Products at the bottom of the funnel.
- Monitor Seasonality: During peak events like Prime Day, ACOS often spikes. Plan for it, and adjust expectations rather than panicking.
When a Higher ACOS is Okay
Not every campaign should aim for the lowest possible ACOS. Sometimes, accepting a higher ACOS is part of a bigger strategy. For example:
- Product launches: Paying more per sale to build reviews and ranking.
- Defensive campaigns: Protecting your brand terms from competitors.
- Awareness building: Running Sponsored Brands or Sponsored Display to expand reach.
In these cases, the higher ACOS is an investment. The long-term gain – organic visibility, repeat purchases, brand recognition – can outweigh the short-term inefficiency.
Balancing Profit and Growth
Smart sellers treat ACOS like a dial, not a destination. You may accept a higher ACOS for some campaigns while keeping others lean and profitable. The balance depends on your wider goals: cash flow, growth trajectory, and competitive landscape.
The danger is chasing “the lowest ACOS” across the board. That can actually limit growth, because you’re cutting back on campaigns that build long-term value.
Final Thoughts
ACOS isn’t a vanity metric – it’s one of the clearest indicators of how efficiently your Amazon ads are working. But context matters. The “right” ACOS depends on your margins, goals, and strategy.
The best approach is balance: know your break-even point, track both ACOS and TACoS, reduce waste where you can, and accept higher ACOS when it fuels growth. Done right, ACOS becomes less of a stress point and more of a tool for decision-making.If you want expert support with optimising campaigns and managing the bigger picture, FNDCommerce offers full Amazon account management solutions so you can keep ACOS under control while scaling sustainably.
